BASH_BUILTINS(1)                                              BASH_BUILTINS(1)



NAME
       bash,  :,  ., [, alias, bg, bind, break, builtin, cd, command, compgen,
       complete, continue, declare, dirs, disown, echo,  enable,  eval,  exec,
       exit,  export,  fc,  fg, getopts, hash, help, history, jobs, kill, let,
       local, logout, popd, printf, pushd, pwd, read, readonly,  return,  set,
       shift,  shopt,  source,  suspend,  test,  times,  trap,  type, typeset,
       ulimit, umask, unalias, unset,  wait  -  bash  built-in  commands,  see
       bash(1)

BASH BUILTIN COMMANDS
       Unless otherwise noted, each builtin command documented in this section
       as accepting options preceded by -- accepts ---- to signify the end of the
       options.   For  example,  the  ::, true, false, and test builtins do not
       accept options.
       :: [arguments]
              No effect; the command does nothing beyond  expanding  arguments
              and  performing any specified redirections.  A zero exit code is
              returned.

        ..  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename  in  the  current  shell
              environment  and return the exit status of the last command exe-
              cuted from filename.  If filename does not contain a slash, file
              names  in  PATH  are used to find the directory containing file-
              name.  The file searched for in PATH  need  not  be  executable.
              When  bash  is  not  in  posix  mode,  the  current directory is
              searched if no file is found in PATH.  If the sourcepath  option
              to  the  shopt  builtin  command  is turned off, the PATH is not
              searched.  If any arguments are supplied, they become the  posi-
              tional  parameters  when  filename  is  executed.  Otherwise the
              positional parameters are unchanged.  The return status  is  the
              status  of  the  last  command exited within the script (0 if no
              commands are executed), and false if filename is  not  found  or
              cannot be read.

       alias [-p] [name[=value] ...]
              Alias with no arguments or with the -p option prints the list of
              aliases in the form alias name=value on standard  output.   When
              arguments  are supplied, an alias is defined for each name whose
              value is given.  A trailing space in  value causes the next word
              to be checked for alias substitution when the alias is expanded.
              For each name in the argument list for which no  value  is  sup-
              plied,  the  name  and  value  of  the  alias is printed.  Alias
              returns true unless a name is given for which no alias has  been
              defined.

       bg [jobspec ...]
              Resume  each  suspended  job jobspec in the background, as if it
              had been started with &&.  If jobspec is not present, the shell's
              notion  of the current job is used.  bg jobspec returns 0 unless
              run when job control is disabled or, when run with  job  control
              enabled,  any  specified  jobspec  was  not found or was started
              without job control.

       bind [-m keymap] [-lpsvPSV]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind readline-command
              Display current readline key and function bindings, bind  a  key
              sequence  to  a  readline  function  or macro, or set a readline
              variable.  Each non-option argument is a  command  as  it  would
              appear  in  .inputrc, but each binding or command must be passed
              as a separate argument; e.g.,  '"\C-x\C-r":  re-read-init-file'.
              Options, if supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
                     and vi-insert.  vi is equivalent to vi-command; emacs  is
                     equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display  readline  function  names and bindings in such a
                     way that they can be re-read.
              -P     List current readline function names and bindings.
              -v     Display readline variable names and values in such a  way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they  can  be  re-
                     read.
              -S     Display  readline  key  sequences bound to macros and the
                     strings they output.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq::shell-command
                     Cause shell-command to be  executed  whenever  keyseq  is
                     entered.

              The  return value is 0 unless an unrecognized option is given or
              an error occurred.

       break [_n]
              Exit from within a for, while, until, or select loop.  If  _n  is
              specified,  break  _n  levels.   _n must be >= 1.  If _n is greater
              than the number of enclosing  loops,  all  enclosing  loops  are
              exited.  The return value is 0 unless the shell is not executing
              a loop when break is executed.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it  arguments,  and
              return its exit status.  This is useful when defining a function
              whose name is the same as a shell builtin, retaining  the  func-
              tionality of the builtin within the function.  The cd builtin is
              commonly redefined this way.  The  return  status  is  false  if
              shell-builtin is not a shell builtin command.

       cd [-L|-P] [dir]
              Change  the  current directory to dir.  The variable HOME is the
              default dir.  The variable CDPATH defines the  search  path  for
              the  directory  containing  dir.  Alternative directory names in
              CDPATH are separated by a colon (:).  A null directory  name  in
              CDPATH  is  the  same as the current directory, i.e., ``..''.  If
              dir begins with a slash (/), then CDPATH is  not  used.  The  -P
              option  says  to use the physical directory structure instead of
              following symbolic links (see also the  -P  option  to  the  set
              builtin command); the -L option forces symbolic links to be fol-
              lowed.  An argument of -- is equivalent to $OLDPWD.   If  a  non-
              empty  directory  name from CDPATH is used, or if -- is the first
              argument, and the directory change is successful,  the  absolute
              pathname of the new working directory is written to the standard
              output.  The return value is true if the directory was  success-
              fully changed; false otherwise.

       caller [expr]
              Returns the context of any active subroutine call (a shell func-
              tion or a script executed with the .. or source builtins.   With-
              out expr, caller displays the line number and source filename of
              the current subroutine call.  If a non-negative integer is  sup-
              plied as expr, caller displays the line number, subroutine name,
              and source file corresponding to that position  in  the  current
              execution  call  stack.  This extra information may be used, for
              example, to print a stack trace.  The current frame is frame  0.
              The  return  value is 0 unless the shell is not executing a sub-
              routine call or expr does not correspond to a valid position  in
              the call stack.

       command [-pVv] command [arg ...]
              Run  command  with  args  suppressing  the normal shell function
              lookup. Only builtin commands or commands found in the PATH  are
              executed.   If the -p option is given, the search for command is
              performed using a default value for PATH that is  guaranteed  to
              find  all  of  the  standard  utilities.  If either the -V or -v
              option is supplied, a description of command is printed.  The -v
              option  causes a single word indicating the command or file name
              used to invoke command to be displayed; the -V option produces a
              more  verbose  description.  If the -V or -v option is supplied,
              the exit status is 0 if command was found, and  1  if  not.   If
              neither option is supplied and an error occurred or command can-
              not be found, the exit status is 127.  Otherwise, the exit  sta-
              tus of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate  possible  completion matches for word according to the
              options, which may  be  any  option  accepted  by  the  complete
              builtin  with  the exception of -p and -r, and write the matches
              to the standard output.  When using the -F or  -C  options,  the
              various  shell  variables  set  by  the  programmable completion
              facilities, while available, will not have useful values.

              The matches will be generated in the same way  as  if  the  pro-
              grammable  completion  code  had  generated them directly from a
              completion specification with the same flags.  If word is speci-
              fied, only those completions matching word will be displayed.

              The  return  value is true unless an invalid option is supplied,
              or no matches were generated.

       complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat]  [-W
       wordlist] [-P prefix] [-S suffix]
              [-X filterpat] [-F function] [-C command] name [name _._._.]
       complete -pr [name ...]
              Specify how arguments to each name should be completed.  If  the
              -p  option  is supplied, or if no options are supplied, existing
              completion specifications are printed in a way that allows  them
              to be reused as input.  The -r option removes a completion spec-
              ification for each name, or, if no names are supplied, all  com-
              pletion specifications.

              The  process  of  applying  these completion specifications when
              word completion is  attempted  is  described  above  under  Pro-
              grammable Completion.

              Other  options,  if specified, have the following meanings.  The
              arguments to the -G, -W, and -X options (and, if necessary,  the
              -P  and -S options) should be quoted to protect them from expan-
              sion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects  of  the  comp-
                      spec's  behavior beyond the simple generation of comple-
                      tions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions
                              if the compspec generates no matches.
                      default Use  readline's  default  filename completion if
                              the compspec generates no matches.
                      dirnames
                              Perform directory name completion if  the  comp-
                              spec generates no matches.
                      filenames
                              Tell  readline that the compspec generates file-
                              names, so it can perform  any  filename-specific
                              processing  (like  adding  a  slash to directory
                              names or suppressing trailing spaces).  Intended
                              to be used with shell functions.
                      nospace Tell   readline  not  to  append  a  space  (the
                              default) to words completed at the  end  of  the
                              line.
                      plusdirs
                              After  any  matches  defined by the compspec are
                              generated,   directory   name   completion    is
                              attempted  and  any  matches  are  added  to the
                              results of the other actions.
              -A action
                      The action may be one of the  following  to  generate  a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names  of  shell  builtin commands.  May also be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also  be
                              specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by
                              the HOSTFILE shell variable.
                      job     Job names, if job control is active.   May  also
                              be specified as -j.
                      keyword Shell  reserved words.  May also be specified as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid  arguments  for  the  -o option to the set
                              builtin.
                      shopt   Shell option names  as  accepted  by  the  shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be spec-
                              ified as -v.
              -G globpat
                      The  filename  expansion  pattern globpat is expanded to
                      generate the possible completions.
              -W wordlist
                      The wordlist is split using the characters  in  the  IFS
                      special  variable as delimiters, and each resultant word
                      is expanded.  The possible completions are  the  members
                      of  the  resultant  list which match the word being com-
                      pleted.
              -C command
                      command is executed in a subshell environment,  and  its
                      output is used as the possible completions.
              -F function
                      The  shell  function function is executed in the current
                      shell environment.  When it finishes, the possible  com-
                      pletions  are  retrieved from the value of the COMPREPLY
                      array variable.
              -X filterpat
                      filterpat is a pattern as used for  filename  expansion.
                      It is applied to the list of possible completions gener-
                      ated by the preceding options and  arguments,  and  each
                      completion  matching filterpat is removed from the list.
                      A leading !! in filterpat negates the  pattern;  in  this
                      case,  any completion not matching filterpat is removed.
              -P prefix
                      prefix is added at the beginning of each  possible  com-
                      pletion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all
                      other options have been applied.

              The return value is true unless an invalid option  is  supplied,
              an  option  other than -p or -r is supplied without a name argu-
              ment, an attempt is made to remove  a  completion  specification
              for a name for which no specification exists, or an error occurs
              adding a completion specification.

       continue [_n]
              Resume the next iteration of the enclosing for, while, until, or
              select  loop.   If  _n  is specified, resume at the _nth enclosing
              loop.  _n must be >= 1.  If _n  is  greater  than  the  number  of
              enclosing  loops,  the  last  enclosing  loop (the ``top-level''
              loop) is resumed.  The return value is 0 unless the shell is not
              executing a loop when continue is executed.

       declare [-afFirtx] [-p] [name[=value] ...]
       typeset [-afFirtx] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are
              given then display the values of variables.  The -p option  will
              display  the  attributes  and  values  of each name.  When -p is
              used, additional options are ignored.  The  -F  option  inhibits
              the  display of function definitions; only the function name and
              attributes are printed.  If the extdebug shell option is enabled
              using  shopt,  the  source  file  name and line number where the
              function is defined  are  displayed  as  well.   The  -F  option
              implies  -f.  The following options can be used to restrict out-
              put to variables with the specified attribute or to  give  vari-
              ables attributes:
              -a     Each name is an array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evalua-
                     tion (see ARITHMETIC EVALUATION )) is performed  when  the
                     variable is assigned a value.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give each name the  trace  attribute.   Traced  functions
                     inherit  the  DEBUG  and  RETURN  traps  from the calling
                     shell.  The trace attribute has no  special  meaning  for
                     variables.
              -x     Mark  names  for  export  to  subsequent commands via the
                     environment.

              Using `+' instead of `-' turns off the attribute  instead,  with
              the  exception that +a may not be used to destroy an array vari-
              able.  When used in a function, makes each name local,  as  with
              the  local  command.   If a variable name is followed by =value,
              the value of the variable is set to value.  The return value  is
              0 unless an invalid option is encountered, an attempt is made to
              define a function using ``-f foo=bar'', an attempt  is  made  to
              assign  a  value  to  a readonly variable, an attempt is made to
              assign a value to an array variable without using  the  compound
              assignment  syntax (see Arrays above), one of the names is not a
              valid shell variable name, an attempt is made to turn off  read-
              only  status for a readonly variable, an attempt is made to turn
              off array status for an array variable, or an attempt is made to
              display a non-existent function with -f.

       dirs [-clpv] [[++_n]] [[--_n]]
              Without  options,  displays  the  list  of  currently remembered
              directories.  The default display  is  on  a  single  line  with
              directory  names  separated by spaces.  Directories are added to
              the list with  the  pushd  command;  the  popd  command  removes
              entries from the list.
              ++_n     Displays the _nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              --_n     Displays  the  _nth  entry  counting from the right of the
                     list shown by dirs when invoked without options, starting
                     with zero.
              -c     Clears  the  directory  stack  by  deleting  all  of  the
                     entries.
              -l     Produces a longer listing;  the  default  listing  format
                     uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print  the  directory stack with one entry per line, pre-
                     fixing each entry with its index in the stack.

              The return value is 0 unless an invalid option is supplied or  _n
              indexes beyond the end of the directory stack.

       disown [-ar] [-h] [jobspec ...]
              Without  options,  each  jobspec  is  removed  from the table of
              active jobs.  If the -h option is given,  each  jobspec  is  not
              removed from the table, but is marked so that SIGHUP is not sent
              to the job if the shell receives a SIGHUP.   If  no  jobspec  is
              present,  and  neither the -a nor the -r option is supplied, the
              current job is used.  If no jobspec is supplied, the  -a  option
              means  to  remove or mark all jobs; the -r option without a job-
              spec argument restricts operation to running jobs.   The  return
              value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output  the  args,  separated  by spaces, followed by a newline.
              The return status is always 0.  If -n is specified, the trailing
              newline  is  suppressed.  If the -e option is given, interpreta-
              tion of the following backslash-escaped characters  is  enabled.
              The  -E option disables the interpretation of these escape char-
              acters, even on systems where they are interpreted  by  default.
              The  xpg_echo  shell option may be used to dynamically determine
              whether or not echo expands these escape characters by  default.
              echo  does  not  interpret  ---- to mean the end of options.  echo
              interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress trailing newline
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\\\     backslash
              \\00nnn  the eight-bit character whose value is  the  octal  value
                     nnn (zero to three octal digits)
              \\nnn   the  eight-bit  character  whose value is the octal value
                     nnn (one to three octal digits)
              \\xx_H_H   the eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits)

       enable [-adnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows a disk command which has the same name as a shell builtin
              to  be  executed without specifying a full pathname, even though
              the shell normally searches for builtins before  disk  commands.
              If  -n  is  used,  each  name  is disabled; otherwise, names are
              enabled.  For example, to use the test binary found via the PATH
              instead  of  the  shell builtin version, run ``enable -n test''.
              The -f option means to load the new builtin  command  name  from
              shared object filename, on systems that support dynamic loading.
              The -d option will delete a builtin previously loaded  with  -f.
              If no name arguments are given, or if the -p option is supplied,
              a list of shell builtins is printed.  With no other option argu-
              ments,  the  list consists of all enabled shell builtins.  If -n
              is supplied, only disabled builtins are printed.  If -a is  sup-
              plied,  the  list printed includes all builtins, with an indica-
              tion of whether or not each is enabled.  If -s is supplied,  the
              output  is restricted to the POSIX special builtins.  The return
              value is 0 unless a name is not a shell builtin or there  is  an
              error loading a new builtin from a shared object.

       eval [arg ...]
              The  args  are read and concatenated together into a single com-
              mand.  This command is then read and executed by the shell,  and
              its  exit status is returned as the value of eval.  If there are
              no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new  process
              is  created.  The arguments become the arguments to command.  If
              the -l option is supplied, the shell places a dash at the begin-
              ning of the zeroth arg passed to command.  This is what login(1)
              does.  The -c option causes command to be executed with an empty
              environment.   If  -a  is supplied, the shell passes name as the
              zeroth argument to the executed command.  If command  cannot  be
              executed  for some reason, a non-interactive shell exits, unless
              the shell option execfail is enabled, in which case  it  returns
              failure.   An interactive shell returns failure if the file can-
              not be executed.  If command is not specified, any  redirections
              take  effect  in  the current shell, and the return status is 0.
              If there is a redirection error, the return status is 1.

       exit [_n]
              Cause the shell to exit with a status of _n.  If  _n  is  omitted,
              the exit status is that of the last command executed.  A trap on
              EXIT is executed before the shell terminates.

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the  envi-
              ronment  of subsequently executed commands.  If the -f option is
              given, the names refer to functions.  If no names are given,  or
              if  the  -p  option  is  supplied,  a list of all names that are
              exported in this shell is printed.  The  -n  option  causes  the
              export  property  to  be  removed from each name.  If a variable
              name is followed by =word, the value of the variable is  set  to
              word.   export  returns  an  exit  status of 0 unless an invalid
              option is encountered, one of the names is  not  a  valid  shell
              variable name, or -f is supplied with a name that is not a func-
              tion.

       fc [-e ename] [-nlr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix Command.  In the first form, a range of commands from  first
              to  last  is selected from the history list.  First and last may
              be specified as a string (to locate the last  command  beginning
              with  that  string)  or  as  a number (an index into the history
              list, where a negative number is used as an offset from the cur-
              rent command number).  If last is not specified it is set to the
              current command for listing (so that ``fc -l  -10''  prints  the
              last 10 commands) and to first otherwise.  If first is not spec-
              ified it is set to the previous command for editing and -16  for
              listing.

              The  -n option suppresses the command numbers when listing.  The
              -r option reverses the order of the commands.  If the -l  option
              is  given,  the  commands are listed on standard output.  Other-
              wise, the editor given by ename is invoked on a file  containing
              those  commands.  If ename is not given, the value of the FCEDIT
              variable is used, and the value of EDITOR if FCEDIT is not  set.
              If  neither variable is set, is used.  When editing is complete,
              the edited commands are echoed and executed.

              In the second form, command is re-executed after  each  instance
              of  pat  is replaced by rep.  A useful alias to use with this is
              ``r="fc -s"'', so that typing ``r c'  runs  the  last  command
              beginning with `c' and typing ``r'' re-executes the last com-
              mand.

              If the first form is used, the  return  value  is  0  unless  an
              invalid  option  is encountered or first or last specify history
              lines out of range.  If the -e option is  supplied,  the  return
              value is the value of the last command executed or failure if an
              error occurs with the temporary file of commands.  If the second
              form  is  used, the return status is that of the command re-exe-
              cuted, unless cmd does not specify  a  valid  history  line,  in
              which case fc returns failure.

       fg [jobspec]
              Resume  jobspec  in the foreground, and make it the current job.
              If jobspec is not present, the shell's notion of the current job
              is  used.   The  return value is that of the command placed into
              the foreground, or failure if run when job control  is  disabled
              or, when run with job control enabled, if jobspec does not spec-
              ify a valid job or jobspec specifies  a  job  that  was  started
              without job control.

       getopts optstring name [args]
              getopts  is used by shell procedures to parse positional parame-
              ters.  optstring contains the option  characters  to  be  recog-
              nized;  if  a  character  is  followed by a colon, the option is
              expected to have an argument, which should be separated from  it
              by  white space.  The colon and question mark characters may not
              be used as option characters.  Each time it is invoked,  getopts
              places  the next option in the shell variable name, initializing
              name if it does not exist, and the index of the next argument to
              be processed into the variable OPTIND.  OPTIND is initialized to
              1 each time the shell or a shell script  is  invoked.   When  an
              option  requires  an argument, getopts places that argument into
              the variable OPTARG.  The shell does not reset OPTIND  automati-
              cally;  it  must  be  manually  reset  between multiple calls to
              getopts within the same shell invocation if a new set of parame-
              ters is to be used.

              When  the  end  of  options is encountered, getopts exits with a
              return value greater than zero.  OPTIND is set to the  index  of
              the first non-option argument, and name is set to ?.

              getopts  normally  parses the positional parameters, but if more
              arguments are given in args, getopts parses those instead.

              getopts can report errors in two ways.  If the  first  character
              of  optstring  is  a  colon, silent error reporting is used.  In
              normal operation diagnostic messages are  printed  when  invalid
              options  or  missing  option  arguments are encountered.  If the
              variable OPTERR is set to 0, no  error  messages  will  be  dis-
              played, even if the first character of optstring is not a colon.

              If an invalid option is seen, getopts places ? into name and, if
              not  silent,  prints  an  error  message  and unsets OPTARG.  If
              getopts is silent, the  option  character  found  is  placed  in
              OPTARG and no diagnostic message is printed.

              If  a required argument is not found, and getopts is not silent,
              a question mark (??) is placed in name, OPTARG is  unset,  and  a
              diagnostic  message  is  printed.   If getopts is silent, then a
              colon (::) is placed in name and OPTARG  is  set  to  the  option
              character found.

              getopts  returns true if an option, specified or unspecified, is
              found.  It returns false if the end of options is encountered or
              an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              For  each  name, the full file name of the command is determined
              by searching the directories in $PATH and remembered.  If the -p
              option is supplied, no path search is performed, and filename is
              used as the full file name of the command.  The -r option causes
              the  shell  to  forget  all remembered locations.  The -d option
              causes the shell to forget the remembered location of each name.
              If  the  -t  option is supplied, the full pathname to which each
              name corresponds is printed.  If  multiple  name  arguments  are
              supplied  with  -t,  the  name is printed before the hashed full
              pathname.  The -l option causes output to be displayed in a for-
              mat  that may be reused as input.  If no arguments are given, or
              if only -l is supplied, information about remembered commands is
              printed.   The  return status is true unless a name is not found
              or an invalid option is supplied.

       help [-s] [pattern]
              Display helpful information about builtin commands.  If  pattern
              is  specified, help gives detailed help on all commands matching
              pattern; otherwise help for all the builtins and  shell  control
              structures  is printed.  The -s option restricts the information
              displayed to a short usage synopsis.  The  return  status  is  0
              unless no command matches pattern.

       history [[_n]]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg _._._.]
       history -s arg [arg _._._.]
              With no options, display the command history list with line num-
              bers.  Lines listed with a ** have been modified.  An argument of
              _n  lists only the last _n lines.  If the shell variable HISTTIME-
              FORMAT is set and not null, it is used as a  format  string  for
              strftime(3)  to display the time stamp associated with each dis-
              played history entry.  No intervening blank is  printed  between
              the  formatted  time stamp and the history line.  If filename is
              supplied, it is used as the name of the history  file;  if  not,
              the  value  of HISTFILE is used.  Options, if supplied, have the
              following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append the ``new'' history lines (history  lines  entered
                     since  the  beginning of the current bash session) to the
                     history file.
              -n     Read the history lines not already read from the  history
                     file  into  the  current  history  list.  These are lines
                     appended to the history file since the beginning  of  the
                     current bash session.
              -r     Read the contents of the history file and use them as the
                     current history.
              -w     Write the current history to the history file,  overwrit-
                     ing the history file's contents.
              -p     Perform  history  substitution  on the following args and
                     display the result on  the  standard  output.   Does  not
                     store  the results in the history list.  Each arg must be
                     quoted to disable normal history expansion.
              -s     Store the args in the history list  as  a  single  entry.
                     The  last  command  in the history list is removed before
                     the args are added.

              If the HISTTIMEFORMAT is set, the time stamp information associ-
              ated  with  each  history  entry is written to the history file.
              The return value is 0 unless an invalid option  is  encountered,
              an  error  occurs  while reading or writing the history file, an
              invalid offset is supplied as an argument to -d, or the  history
              expansion supplied as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the fol-
              lowing meanings:
              -l     List process IDs in addition to the normal information.
              -p     List only the process  ID  of  the  job's  process  group
                     leader.
              -n     Display  information  only  about  jobs that have changed
                     status since the user was last notified of their  status.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

              If  jobspec  is given, output is restricted to information about
              that job.  The return status is 0 unless an  invalid  option  is
              encountered or an invalid jobspec is supplied.

              If the -x option is supplied, jobs replaces any jobspec found in
              command or args with the corresponding  process  group  ID,  and
              executes command passing it args, returning its exit status.

       kill [-s sigspec | -n signum | --sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit__status]
              Send  the  signal  named  by  sigspec or signum to the processes
              named by pid or jobspec.  sigspec is either  a  case-insensitive
              signal  name such as SIGKILL (with or without the SIG prefix) or
              a signal number; signum is a signal number.  If sigspec  is  not
              present,  then  SIGTERM is assumed.  An argument of -l lists the
              signal names.  If any arguments are supplied when -l  is  given,
              the  names  of  the  signals  corresponding to the arguments are
              listed, and the return status is 0.  The exit__status argument to
              -l  is  a  number  specifying either a signal number or the exit
              status of a process terminated by a signal.  kill  returns  true
              if  at  least  one  signal was successfully sent, or false if an
              error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each arg is an arithmetic expression to be evaluated (see ARITH-
              METIC  EVALUATION).  If the last arg evaluates to 0, let returns
              1; 0 is returned otherwise.

       local [option] [name[=value] ...]
              For each argument, a local variable named name is  created,  and
              assigned  value.   The option can be any of the options accepted
              by declare.  When local is used within a function, it causes the
              variable  name  to have a visible scope restricted to that func-
              tion and its children.  With no operands, local writes a list of
              local  variables  to the standard output.  It is an error to use
              local when not within a function.  The return status is 0 unless
              local  is  used outside a function, an invalid name is supplied,
              or name is a readonly variable.

       logout Exit a login shell.

       popd [-nn] [+_n] [-_n]
              Removes entries from the directory stack.   With  no  arguments,
              removes  the  top directory from the stack, and performs a cd to
              the new top directory.  Arguments, if supplied, have the follow-
              ing meanings:
              ++_n     Removes  the _nth entry counting from the left of the list
                     shown by dirs, starting with zero.  For  example:  ``popd
                     +0'' removes the first directory, ``popd +1'' the second.
              --_n     Removes the _nth entry counting from the right of the list
                     shown  by  dirs, starting with zero.  For example: ``popd
                     -0'' removes the last directory, ``popd -1'' the next  to
                     last.
              -n     Suppresses  the  normal change of directory when removing
                     directories from the stack, so that  only  the  stack  is
                     manipulated.

              If  the popd command is successful, a dirs is performed as well,
              and the return status is 0.  popd returns false  if  an  invalid
              option is encountered, the directory stack is empty, a non-exis-
              tent directory stack entry is specified, or the directory change
              fails.

       printf [-v var] format [arguments]
              Write  the  formatted arguments to the standard output under the
              control of the format.  The format is a character  string  which
              contains  three  types  of  objects: plain characters, which are
              simply copied to standard output,  character  escape  sequences,
              which  are converted and copied to the standard output, and for-
              mat specifications, each of which causes printing  of  the  next
              successive argument.  In addition to the standard printf(1) for-
              mats, %b causes printf to expand backslash escape  sequences  in
              the  corresponding  argument  (except that \c terminates output,
              backslashes in \\'', \\"", and \\?? are not removed, and octal escapes
              beginning  with \\00 may contain up to four digits), and %q causes
              printf to output the corresponding argument in a format that can
              be reused as shell input.

              The  -v  option causes the output to be assigned to the variable
              var rather than being printed to the standard output.

              The format is reused as necessary to consume all  of  the  argu-
              ments.  If the format requires more arguments than are supplied,
              the extra format specifications behave as if  a  zero  value  or
              null  string,  as  appropriate,  had  been supplied.  The return
              value is zero on success, non-zero on failure.

       pushd [-n] [dir]
       pushd [-n] [+_n] [-_n]
              Adds a directory to the top of the directory stack,  or  rotates
              the  stack,  making the new top of the stack the current working
              directory.  With no arguments, exchanges the top two directories
              and  returns 0, unless the directory stack is empty.  Arguments,
              if supplied, have the following meanings:
              ++_n     Rotates the stack so that  the  _nth  directory  (counting
                     from  the  left  of the list shown by dirs, starting with
                     zero) is at the top.
              --_n     Rotates the stack so that  the  _nth  directory  (counting
                     from  the  right of the list shown by dirs, starting with
                     zero) is at the top.
              -n     Suppresses the normal change  of  directory  when  adding
                     directories  to  the  stack,  so  that  only the stack is
                     manipulated.
              dir    Adds dir to the directory stack at the top, making it the
                     new current working directory.

              If the pushd command is successful, a dirs is performed as well.
              If the first form is used, pushd returns 0 unless the cd to  dir
              fails.   With the second form, pushd returns 0 unless the direc-
              tory stack is empty, a non-existent directory stack  element  is
              specified,  or the directory change to the specified new current
              directory fails.

       pwd [-LP]
              Print the absolute pathname of the  current  working  directory.
              The pathname printed contains no symbolic links if the -P option
              is supplied or the -o physical option to the set builtin command
              is  enabled.  If the -L option is used, the pathname printed may
              contain symbolic links.  The return status is 0 unless an  error
              occurs  while  reading  the  name of the current directory or an
              invalid option is supplied.

       read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d
       delim] [name ...]
              One line is read from the  standard  input,  or  from  the  file
              descriptor  fd supplied as an argument to the -u option, and the
              first word is assigned to the first name, the second word to the
              second  name, and so on, with leftover words and their interven-
              ing separators assigned to the last name.  If  there  are  fewer
              words read from the input stream than names, the remaining names
              are assigned empty values.  The characters in IFS  are  used  to
              split  the  line into words.  The backslash character (\\) may be
              used to remove any special meaning for the next  character  read
              and  for line continuation.  Options, if supplied, have the fol-
              lowing meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.   Other  name  arguments  are
                     ignored.
              -d delim
                     The  first  character  of  delim is used to terminate the
                     input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline
                     (see READLINE above) is used to obtain the line.
              -n nchars
                     read  returns after reading nchars characters rather than
                     waiting for a complete line of input.
              -p prompt
                     Display prompt on standard error, without a trailing new-
                     line, before attempting to read any input.  The prompt is
                     displayed only if input is coming from a terminal.
              -r     Backslash does not act as an escape character.  The back-
                     slash  is considered to be part of the line.  In particu-
                     lar, a backslash-newline pair may not be used as  a  line
                     continuation.
              -s     Silent mode.  If input is coming from a terminal, charac-
                     ters are not echoed.
              -t timeout
                     Cause read to time out and return failure if  a  complete
                     line  of  input is not read within timeout seconds.  This
                     option has no effect if read is not  reading  input  from
                     the terminal or a pipe.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the vari-
              able REPLY.  The return code  is  zero,  unless  end-of-file  is
              encountered,  read  times  out, or an invalid file descriptor is
              supplied as the argument to -u.

       readonly [-apf] [name[=word] ...]
              The given names are marked readonly; the values of  these  names
              may  not  be changed by subsequent assignment.  If the -f option
              is supplied, the functions corresponding to  the  names  are  so
              marked.  The -a option restricts the variables to arrays.  If no
              name arguments are given, or if the -p  option  is  supplied,  a
              list  of  all  readonly  names is printed.  The -p option causes
              output to be displayed in a format that may be reused as  input.
              If  a variable name is followed by =word, the value of the vari-
              able is set to word.  The return status is 0 unless  an  invalid
              option  is  encountered,  one  of the names is not a valid shell
              variable name, or -f is supplied with a name that is not a func-
              tion.

       return [_n]
              Causes  a function to exit with the return value specified by _n.
              If _n is omitted, the return status is that of the  last  command
              executed  in the function body.  If used outside a function, but
              during execution of a script by  the  ..   (source)  command,  it
              causes the shell to stop executing that script and return either
              _n or the exit status of the last  command  executed  within  the
              script  as  the  exit  status  of the script.  If used outside a
              function and not during execution of a script by ..,  the  return
              status is false.  Any command associated with the RETURN trap is
              executed before execution resumes after the function or  script.

       set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
              Without  options,  the name and value of each shell variable are
              displayed in a format that can be reused as input for setting or
              resetting the currently-set variables.  Read-only variables can-
              not be reset.  In posix mode, only shell variables  are  listed.
              The  output  is  sorted  according  to the current locale.  When
              options are specified, they set or unset shell attributes.   Any
              arguments  remaining after the options are processed are treated
              as values for the positional parameters  and  are  assigned,  in
              order, to $$11, $$22, ......  $$_n.  Options, if specified, have the fol-
              lowing meanings:
              -a      Automatically mark variables  and  functions  which  are
                      modified  or  created  for  export to the environment of
                      subsequent commands.
              -b      Report the status of terminated background jobs  immedi-
                      ately, rather than before the next primary prompt.  This
                      is effective only when job control is enabled.
              -e      Exit immediately if a simple command (see SHELL  GRAMMAR
                      above) exits with a non-zero status.  The shell does not
                      exit if the command that fails is part  of  the  command
                      list  immediately  following  a  while or until keyword,
                      part of the test in an if statement, part of a &&&& or  ||||
                      list, or if the command's return value is being inverted
                      via !!.  A trap on ERR, if set, is  executed  before  the
                      shell exits.
              -f      Disable pathname expansion.
              -h      Remember  the location of commands as they are looked up
                      for execution.  This is enabled by default.
              -k      All arguments in the form of assignment  statements  are
                      placed  in the environment for a command, not just those
                      that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This  option  is
                      on  by  default  for  interactive shells on systems that
                      support it (see JOB  CONTROL  above).   Background  pro-
                      cesses  run  in a separate process group and a line con-
                      taining their exit status is printed upon their  comple-
                      tion.
              -n      Read commands but do not execute them.  This may be used
                      to check a shell script  for  syntax  errors.   This  is
                      ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use  an  emacs-style command line editing inter-
                              face.  This is enabled by default when the shell
                              is interactive, unless the shell is started with
                              the --noediting option.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      errexit Same as -e.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under
                              HISTORY.  This option is on by default in inter-
                              active shells.
                      ignoreeof
                              The  effect  is  as   if   the   shell   command
                              ``IGNOREEOF=10''  had  been  executed (see Shell
                              Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.  nolog Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a  pipeline  is  the
                              value  of  the  last (rightmost) command to exit
                              with a non-zero status, or zero if all  commands
                              in  the pipeline exit successfully.  This option
                              is disabled by default.
                      posix   Change the behavior of bash  where  the  default
                              operation differs from the POSIX 1003.2 standard
                              to match the standard (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of the
                      current  options are printed.  If +o is supplied with no
                      option-name, a series of set commands  to  recreate  the
                      current  option  settings  is  displayed on the standard
                      output.
              -p      Turn on privileged mode.  In this  mode,  the  $ENV  and
                      $BASH_ENV  files  are not processed, shell functions are
                      not inherited from the environment,  and  the  SHELLOPTS
                      variable,  if it appears in the environment, is ignored.
                      If the shell is started with the effective user  (group)
                      id  not  equal  to  the real user (group) id, and the -p
                      option is not supplied, these actions are taken and  the
                      effective user id is set to the real user id.  If the -p
                      option is supplied at startup, the effective user id  is
                      not reset.  Turning this option off causes the effective
                      user and group ids to be set to the real user and  group
                      ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables as an error when performing param-
                      eter expansion.  If expansion is attempted on  an  unset
                      variable, the shell prints an error message, and, if not
                      interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for  command,  case
                      command, select command, or arithmetic for command, dis-
                      play the expanded value of PS4, followed by the  command
                      and its expanded arguments or associated word list.
              -B      The  shell performs brace expansion (see Brace Expansion
                      above).  This is on by default.
              -C      If set, bash does not overwrite an  existing  file  with
                      the  >>,  >>&&,  and <<>> redirection operators.  This may be
                      overridden when creating output files by using the redi-
                      rection operator >>|| instead of >>.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command substitutions, and commands executed in  a  sub-
                      shell  environment.  The ERR trap is normally not inher-
                      ited in such cases.
              -H      Enable !!  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If  set,  the  shell does not follow symbolic links when
                      executing commands such as cd that  change  the  current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain  of  directories  when  performing  commands which
                      change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by
                      shell  functions,  command  substitutions,  and commands
                      executed in  a  subshell  environment.   The  DEBUG  and
                      RETURN traps are normally not inherited in such cases.
              ----      If  no arguments follow this option, then the positional
                      parameters are unset.  Otherwise, the positional parame-
                      ters  are  set  to  the args, even if some of them begin
                      with a --.
              --       Signal the end of options, cause all remaining  args  to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the posi-
                      tional parameters remain unchanged.

              The  options are off by default unless otherwise noted.  Using +
              rather than - causes  these  options  to  be  turned  off.   The
              options  can  also be specified as arguments to an invocation of
              the shell.  The current set of options may be found in $$--.   The
              return status is always true unless an invalid option is encoun-
              tered.

       shift [_n]
              The positional parameters from _n+1 ... are renamed  to  $$11  ........
              Parameters  represented  by  the  numbers  $$## down to $$##-_n+1 are
              unset.  _n must be a non-negative number less than  or  equal  to
              $$##.   If  _n is 0, no parameters are changed.  If _n is not given,
              it is assumed to be 1.  If _n is greater than $$##, the  positional
              parameters  are  not changed.  The return status is greater than
              zero if _n is greater than $$## or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of variables controlling optional shell behav-
              ior.  With no options, or with the -p option, a list of all set-
              table options is displayed, with an indication of whether or not
              each  is  set.  The -p option causes output to be displayed in a
              form that may be reused as input.  Other options have  the  fol-
              lowing meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status
                     indicates whether the optname is set or unset.  If multi-
                     ple  optname arguments are given with -q, the return sta-
                     tus is zero if all optnames are enabled; non-zero  other-
                     wise.
              -o     Restricts  the  values of optname to be those defined for
                     the -o option to the set builtin.

              If either -s or -u is used with no optname arguments,  the  dis-
              play is limited to those options which are set or unset, respec-
              tively.  Unless otherwise noted, the shopt options are  disabled
              (unset) by default.

              The  return  status when listing options is zero if all optnames
              are enabled, non-zero  otherwise.   When  setting  or  unsetting
              options,  the  return  status is zero unless an optname is not a
              valid shell option.

              The list of shopt options is:

              cdable_vars
                      If set, an argument to the cd builtin  command  that  is
                      not  a directory is assumed to be the name of a variable
                      whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory com-
                      ponent  in  a  cd command will be corrected.  The errors
                      checked for are transposed characters, a missing charac-
                      ter,  and  one  character  too many.  If a correction is
                      found, the corrected file name is printed, and the  com-
                      mand  proceeds.  This option is only used by interactive
                      shells.
              checkhash
                      If set, bash checks that a command found in the hash ta-
                      ble  exists  before  trying  to execute it.  If a hashed
                      command no longer exists, a normal path search  is  per-
                      formed.
              checkwinsize
                      If  set,  bash checks the window size after each command
                      and, if necessary, updates the values of LINES and  COL-
                      UMNS.
              cmdhist If  set,  bash attempts to save all lines of a multiple-
                      line command in the same  history  entry.   This  allows
                      easy re-editing of multi-line commands.
              dotglob If  set, bash includes filenames beginning with a `.' in
                      the results of pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not  execute  the  file  specified as an argument to the
                      exec builtin command.  An  interactive  shell  does  not
                      exit if exec fails.
              expand_aliases
                      If  set,  aliases  are expanded as described above under
                      ALIASES.  This option is enabled by default for interac-
                      tive shells.
              extdebug
                      If  set,  behavior  intended  for  use  by  debuggers is
                      enabled:
                      11..     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      22..     If the command run by the DEBUG  trap  returns  a
                             non-zero  value,  the next command is skipped and
                             not executed.
                      33..     If the command run by the DEBUG  trap  returns  a
                             value  of 2, and the shell is executing in a sub-
                             routine (a shell function or a shell script  exe-
                             cuted  by  the  ..  or source builtins), a call to
                             return is simulated.
                      44..     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions above.
                      55..     Function  tracing  is enabled:  command substitu-
                             tion, shell functions, and subshells invoked with
                             (( command )) inherit the DEBUG and RETURN traps.
                      66..     Error  tracing is enabled:  command substitution,
                             shell functions, and  subshells  invoked  with  ((
                             command )) inherit the ERROR trap.
              extglob If set, the extended pattern matching features described
                      above under Pathname Expansion are enabled.
              extquote
                      If set, $$'string' and  $$"string"  quoting  is  performed
                      within   $${{parameter}}   expansions  enclosed  in  double
                      quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to  match  filenames  during
                      pathname expansion result in an expansion error.
              force_fignore
                      If  set,  the  suffixes  specified  by the FIGNORE shell
                      variable cause words to be ignored when performing  word
                      completion even if the ignored words are the only possi-
                      ble  completions.   See  SHELL  VARIABLES  above  for  a
                      description  of  FIGNORE.   This  option  is  enabled by
                      default.
              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.
              histappend
                      If  set,  the history list is appended to the file named
                      by the value of the HISTFILE  variable  when  the  shell
                      exits, rather than overwriting the file.
              histreedit
                      If  set, and readline is being used, a user is given the
                      opportunity to re-edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of  his-
                      tory  substitution  are  not  immediately  passed to the
                      shell parser.  Instead, the  resulting  line  is  loaded
                      into the readline editing buffer, allowing further modi-
                      fication.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform  hostname  completion when a word containing a @@
                      is  being  completed  (see  Completing  under   READLINE
                      above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an inter-
                      active login shell exits.
              interactive_comments
                      If set, allow a word beginning with ## to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive  shell  (see  COMMENTS  above).   This
                      option is enabled by default.
              lithist If  set,  and  the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              login_shell
                      The  shell  sets this option if it is started as a login
                      shell (see INVOCATION above).   The  value  may  not  be
                      changed.
              mailwarn
                      If  set,  and  a file that bash is checking for mail has
                      been accessed since the last time it  was  checked,  the
                      message  ``The  mail in mailfile has been read'' is dis-
                      played.
              no_empty_cmd_completion
                      If set, and  readline  is  being  used,  bash  will  not
                      attempt to search the PATH for possible completions when
                      completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches  filenames  in  a  case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).
              nocasematch
                      If set, bash  matches  patterns  in  a  case-insensitive
                      fashion when performing matching while executing case or
                      [[[[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no  files  (see
                      Pathname  Expansion  above)  to expand to a null string,
                      rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Pro-
                      grammable Completion above) are enabled.  This option is
                      enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand   substitution,  arithmetic  expansion,  and  quote
                      removal after being expanded as described  in  PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The   shell  sets  this  option  if  it  is  started  in
                      restricted mode (see RESTRICTED SHELL below).  The value
                      may  not be changed.  This is not reset when the startup
                      files are executed, allowing the startup files  to  dis-
                      cover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the shift builtin prints an error message when
                      the shift count exceeds the number of positional parame-
                      ters.
              sourcepath
                      If set, the source (..) builtin uses the value of PATH to
                      find the directory containing the file  supplied  as  an
                      argument.  This option is enabled by default.
              xpg_echo
                      If   set,  the  echo  builtin  expands  backslash-escape
                      sequences by default.
       suspend [-f]
              Suspend the execution of this shell until it receives a  SIGCONT
              signal.   The  -f option says not to complain if this is a login
              shell; just suspend anyway.  The return status is 0  unless  the
              shell is a login shell and -f is not supplied, or if job control
              is not enabled.
       test expr
       [[ expr ]]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expr.  Each operator and operand must be
              a separate argument.  Expressions are composed of the  primaries
              described  above  under  CONDITIONAL EXPRESSIONS.  test does not
              accept any options, nor does it accept and ignore an argument of
              ---- as signifying the end of options.

              Expressions  may  be  combined  using  the  following operators,
              listed in decreasing order of precedence.
              !! expr True if expr is false.
              (( expr ))
                     Returns the value of expr.  This may be used to  override
                     the normal precedence of operators.
              expr1 -aa expr2
                     True if both expr1 and expr2 are true.
              expr1 -oo expr2
                     True if either expr1 or expr2 is true.

              test and [[ evaluate conditional expressions using a set of rules
              based on the number of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not
                     null.
              2 arguments
                     If the first argument is !!, the expression is true if and
                     only if the second argument is null.  If the first  argu-
                     ment  is  one  of  the unary conditional operators listed
                     above under CONDITIONAL EXPRESSIONS,  the  expression  is
                     true if the unary test is true.  If the first argument is
                     not a valid unary conditional operator, the expression is
                     false.
              3 arguments
                     If  the  second argument is one of the binary conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the
                     result of the expression is the result of the binary test
                     using the first and third arguments as operands.  If  the
                     first  argument  is  !!,  the value is the negation of the
                     two-argument test using the second and  third  arguments.
                     If the first argument is exactly (( and the third argument
                     is exactly )), the result is the one-argument test of  the
                     second  argument.   Otherwise,  the  expression is false.
                     The -a and -o operators are considered  binary  operators
                     in this case.
              4 arguments
                     If the first argument is !!, the result is the negation of
                     the three-argument expression composed of  the  remaining
                     arguments.  Otherwise, the expression is parsed and eval-
                     uated according to  precedence  using  the  rules  listed
                     above.
              5 or more arguments
                     The  expression  is  parsed  and  evaluated  according to
                     precedence using the rules listed above.

       times  Print the accumulated user and system times for  the  shell  and
              for processes run from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The  command  arg  is  to  be  read  and executed when the shell
              receives signal(s) sigspec.  If arg is absent (and  there  is  a
              single  sigspec)  or  --,  each  specified signal is reset to its
              original disposition (the value it  had  upon  entrance  to  the
              shell).   If arg is the null string the signal specified by each
              sigspec is ignored by the shell and by the commands it  invokes.
              If  arg  is  not present and -p has been supplied, then the trap
              commands associated with each  sigspec  are  displayed.   If  no
              arguments  are  supplied or if only -p is given, trap prints the
              list of commands associated with each  signal.   The  -l  option
              causes  the shell to print a list of signal names and their cor-
              responding numbers.   Each  sigspec  is  either  a  signal  name
              defined  in  <signal.h>,  or  a signal number.  Signal names are
              case insensitive and the SIG prefix is optional.  If  a  sigspec
              is  EXIT (0) the command arg is executed on exit from the shell.
              If a sigspec is DEBUG, the command arg is executed before  every
              simple command, for command, case command, select command, every
              arithmetic for command, and before the first command executes in
              a  shell  function  (see  SHELL  GRAMMAR  above).   Refer to the
              description of the extdebug option  to  the  shopt  builtin  for
              details  of  its effect on the DEBUG trap.  If a sigspec is ERR,
              the command arg is executed whenever  a  simple  command  has  a
              non-zero  exit status, subject to the following conditions.  The
              ERR trap is not executed if the failed command is  part  of  the
              command  list  immediately  following  a while or until keyword,
              part of the test in an if statement, part of a &&&& or |||| list, or
              if  the  command's  return value is being inverted via !!.  These
              are the same conditions obeyed by  the  errexit  option.   If  a
              sigspec is RETURN, the command arg is executed each time a shell
              function or a script executed with the .. or source builtins fin-
              ishes executing.  Signals ignored upon entry to the shell cannot
              be trapped or reset.  Trapped signals are reset to their  origi-
              nal  values  in  a child process when it is created.  The return
              status is false  if  any  sigspec  is  invalid;  otherwise  trap
              returns true.

       type [-aftpP] name [name ...]
              With  no options, indicate how each name would be interpreted if
              used as a command name.  If the -t option is used, type prints a
              string  which  is  one  of alias, keyword, function, builtin, or
              file if  name  is  an  alias,  shell  reserved  word,  function,
              builtin,  or disk file, respectively.  If the name is not found,
              then nothing  is  printed,  and  an  exit  status  of  false  is
              returned.   If  the  -p  option is used, type either returns the
              name of the disk file that would be executed if name were speci-
              fied as a command name, or nothing if ``type -t name'' would not
              return file.  The -P option forces a PATH search for each  name,
              even if ``type -t name'' would not return file.  If a command is
              hashed, -p and -P print the hashed value,  not  necessarily  the
              file that appears first in PATH.  If the -a option is used, type
              prints all of the places that contain an executable named  name.
              This  includes  aliases  and  functions,  if  and only if the -p
              option is not also used.  The table of hashed  commands  is  not
              consulted  when  using -a.  The -f option suppresses shell func-
              tion lookup, as with the command builtin.  type returns true  if
              any of the arguments are found, false if none are found.

       ulimit [-SHacdflmnpstuv [limit]]
              Provides  control  over the resources available to the shell and
              to processes started by it, on systems that allow such  control.
              The -H and -S options specify that the hard or soft limit is set
              for the given resource.  A hard limit cannot be  increased  once
              it  is set; a soft limit may be increased up to the value of the
              hard limit.  If neither -H nor -S is specified,  both  the  soft
              and  hard limits are set.  The value of limit can be a number in
              the unit specified for the resource or one of the special values
              hard,  soft,  or  unlimited,  which  stand  for the current hard
              limit, the current soft limit, and no limit,  respectively.   If
              limit  is  omitted,  the  current value of the soft limit of the
              resource is printed, unless the -H option is given.   When  more
              than  one  resource  is  specified,  the limit name and unit are
              printed before the value.  Other options are interpreted as fol-
              lows:
              -a     All current limits are reported
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -f     The maximum size of files created by the shell
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes  available  to  a  single
                     user
              -v     The  maximum  amount  of  virtual memory available to the
                     shell

              If limit is given, it is the new value of the specified resource
              (the -a option is display only).  If no option is given, then -f
              is assumed.  Values are in 1024-byte increments, except for  -t,
              which  is  in seconds, -p, which is in units of 512-byte blocks,
              and -n and -u, which are unscaled values.  The return status  is
              0  unless an invalid option or argument is supplied, or an error
              occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with
              a  digit,  it is interpreted as an octal number; otherwise it is
              interpreted as a symbolic mode mask similar to that accepted  by
              chmod(1).   If mode is omitted, the current value of the mask is
              printed.  The -S option causes the mask to be  printed  in  sym-
              bolic  form;  the  default output is an octal number.  If the -p
              option is supplied, and mode is omitted, the output is in a form
              that may be reused as input.  The return status is 0 if the mode
              was successfully changed or if no mode  argument  was  supplied,
              and false otherwise.

       unalias [-aa] [name ...]
              Remove  each  name  from  the list of defined aliases.  If -a is
              supplied, all alias definitions are removed.  The  return  value
              is true unless a supplied name is not a defined alias.

       unset [-fv] [name ...]
              For  each  name,  remove the corresponding variable or function.
              If no options are supplied, or the -v option is given, each name
              refers  to  a  shell  variable.   Read-only variables may not be
              unset.  If -f is specified, each name refers to  a  shell  func-
              tion,  and the function definition is removed.  Each unset vari-
              able or function is removed from the environment passed to  sub-
              sequent  commands.   If any of RANDOM, SECONDS, LINENO, HISTCMD,
              FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special
              properties,  even if they are subsequently reset.  The exit sta-
              tus is true unless a name is readonly.

       wait [_n _._._.]
              Wait for each specified process and return its termination  sta-
              tus.   Each  _n  may be a process ID or a job specification; if a
              job spec is given, all processes  in  that  job's  pipeline  are
              waited  for.  If _n is not given, all currently active child pro-
              cesses are waited for, and the return  status  is  zero.   If  _n
              specifies  a  non-existent  process or job, the return status is
              127.  Otherwise, the return status is the  exit  status  of  the
              last process or job waited for.

SEE ALSO
       bash(1), sh(1)



GNU Bash-3.0                      2004 Apr 20                 BASH_BUILTINS(1)
